Inducers for centrifugal pumps

ABSTRACT

A CENTRIFUGAL PUMP INDUCER COMPOSED OF A NUMBER OF BLADE SETS WITH CONSECUTIVELY INCREASING DIAMETERS, EACH SET   OF BLADES BEING CAPABLE OF INCREASING THE ENERGY OF THE PUMPED FLUID.

ited States Patent lnventor Shmarlahu Yedldiah 89 Oakridge Road, WestOrange, NJ. 07052 Appl. No. 851,201

Filed Aug. 19, 1969 Patented June 28, 1971 INDUCERS FOR CENTRIFUGALPUMPS [56] References Cited UNITED STATES PATENTS 2,016,831 10/1935Havill 415/143 1,878,907 9/1932 Staats, Jr. 416/200 2,509,442 5/1950Matheisel 103/115X 2,555,619 6/1951 Vincent 103/115X 2,984,189 5/1961Jekat 103/88 3,102,481 9/1963 Stoner et a1 103/5 3,163,119 12/1964Huppert et a1. i 103/89 3,200,753 8/1965 Stefano et a1. 103/87 PrimaryExaminer-Leonard H. Ger-in ABSTRACT: A centrifugal pump inducer composedof a number of blade sets with consecutively increasing diameters, eachset of blades being capable of increasing the energy of the pumpedfluid.

PATENTEUJUN28I97I INDUCERS FOR CENTRIFUGAL PUMPS This invention relatesto inducers for centrifugal pumps and is intended to help overcome someof the shortcomings which are usually encountered with conventionalinducers.

Conventional inducers are, generally, axial or mixed-flow impellers withan high solidity of the blades and low blade angles. This type ofinducers is subjected, often, to the following shortcomings:

a. It requires extra space ahead of the main pump impeller.

b. It often requires to be made of a greater diameter than the eye ofthe pump impeller. Conversely, if we make them of the same diameter asthe eye of the impeller, we have to choose higher angles, to enable theinducer to handle the full capacity of the pump. An increase of theblade angles of the inducer, however, increases the NPSH requirements ofthe unit.

0. An increased diameter of the inducer increases the relative velocitybetween the outer tips of the blades and the liquid. This againincreases the NPSH requirements of the inducer.

d. The conventional inducer has, usually, relatively long blades. Thisenables the vapor bubbles, which are created during cavitation, tocollect in the long passages between the blades and to block offcompletely the passage of the liquid.

e. During partial cavitation, there may happen that cavities will formonly in some of the passages. As this is usually an unstable condition,so these cavities will travel from passage to passage, giving rise tonoise and vibrations.

f. The conventional inducer operates satisfactorily only over a verylimited range of flow rates.

g. Each inducer has to be designed specifically for a given impeller, tobe able to operate satisfactorily. Even in this case, the conventionalinducer is capable to reduce the NPSH requirements only over a verylimited range of flow rates, as pointed out under point (g).

The present invention is capable to eliminate, almost completely, theshortcomings listed under (a) to (c) inclusively. Besides this, it iscapable to reduce significantly the shortcomings listed under (d) to (g)inclusively.

A schematical presentation of my invention is given in the drawing inwhich:

FIG. 1 is a schematical section of an arrangement in which the induceris located ahead of the main pump impeller.

FIG. 2 is a schematical section of an arrangement in which the induceris located, partially, within the eye of the impeller.

FIG. 3 presents the plan of an inducer provided with three sets ofvanes, viewed from the direction of the incoming liquid.

The inducer consists, essentially, of an hub 4, to which there isattached a series of sets of blades. The first three of these sets aredenoted on the drawing by the numbers 1, 2, and 3.

In practice, there may be more than three sets of blades or less,depending upon the duties for which a given inducer is designed.

The set number one is the set which comes first in contact with theincoming liquid. This set has the smallest diameter of all. The nextset, marked by the number 2, is of a somewhat greater diameter. The setmarked 3 is of a greater diameter than the set marked 2, and eachsubsequent set is greater than its predecessor.

As the set marked by the number 1 has a very small diameter, thereforeits peripheral speed is also very small. This allows the set to handleliquids at considerably lower NPSH, than it is possible with an inducerwhich has a diameter equal to, or greater than the eye of the main pumpimpeller 5.

The part of the liquid which was acted upon by the set 1 of the bladeswill gain a certain amount of energy. A part of this high-energy liquidwill flow back into the suction line, but the remainder will mix withthe rest of the incoming liquid, thus increasing the available NPSH ofthe liquid which enters the set 2 of the blades. Because of thisincrease in the available NPSH, the set 2 of the blades can now be madewith a greater diameter than set 1: without impairing the effectivenessof the inducer.

The same procedure is repeated when the liquid passes through the set 2of the blades. Still more energy is added to the flowing liquid, thusincreasing still more the available NPSH. The liquid can now be handledsafely by the set 3 of the blades, which is of a greater diameter thanset 2.

This procedure can be repeated so many times, until the liquid acquiresenough energy to be handled directly by the pump impeller 5.

Of course, the efficiency of such as inducer, due to the greatclearances between the vane tips and the walls of the casing, will besmall. However, experience with the Wemco" type sewage pumps shows us,that it is possible to attain acceptable efficiencies even in the casewhen there exists very great clearances between the blades and thecasing. Besides this, an inducer is generally designed to perform only asmall part of the total work which has to be performed by the inducerpump combination. Because of this, the low efficiency of an inducer willreduce only slightly the overall'efficiency of the total pumping unit.

Comparing now the features of this invention with the shortcomings ofthe conventional inducers, we see that:

a. As there exist, generally, generous clearances between the blade tipsand the casing, and as there exists a possibility to make the blades ofthis inducer much narrower than the blades of a conventional inducer,therefore the new inducer offers a considerably smaller obstruction tothe flow of the liquid than a conventional inducer. This allows to placethe inducer described in this specification partially, and sometimeseven wholly, inside the eye of the pump impeller, as sown in FIG. 2.

b. As the inducer described in this specification can be designed insuch a manner, as to form only a small obstruction to the flow of theliquid, therefore there is no need to make the diameter of the passage,where the inducer is located, greater than the diameter of the eye ofthe pump impeller 5.

c. As the first set of blades of this inducer can be made very small,therefore this inducer is capable to handle liquids at lower availableNPSH than an inducer which outer diameter is equal, or even greater thanthe eye of the main pump impeller.

d. As the blades of each set can be made narrow, there is very littlespace available, where vapor bubbles could collect and shut off the flowof the liquid.

e. With narrow blades, there is less probability for vapor bubbles toclog up even a part of the passages. Besides this, any instabilities dueto partial cavitation can be counteracted by designing each set ofblades with a different number of blades. This can enable to eliminateany resonance in relation to the frequency of these instabilities.

f. As the inducer described in this specification is capable to addenergy to the incoming liquid, without forcing it to flow throughconfined passages, therefore such an inducer may be applicable to awider range of fiow rates and to more pump sizes than a conventionalinducer.

g. When we place such an inducer ahead of the impeller, then thereexists a possibility to reduce the backflow of the liquid, by installingstationary vanes in the surrounding casing. Such blades are capable toincrease the efficiency of this type of inducers.

Iclaim:

1. An inducer composed ofa number of blade-sets with consecutivelyincreasing diameters, arranged in such a manner, that the energy of theliquid which passes through any set is increased, before the liquidenters the consecutive set with the larger diameter.

2. An inducer as claimed under claim 1, with sets of axial flow blades.

3. An inducer as claimed under claim 1, provided with sets ofmixed-flowblades.

4. An inducer as claimed under claim 1, composed of a combination ofaxial flow and of mixed-flow blades.

5. An inducer as claimed under claim 1, in which the casing is providedwith additional stationary guide-vanes.

the eye of the impeller.

10. An inducer as claimed under claim I, mounted partially or whollywithin the eye ofthe impeller.

11. An inducer. as claimed under claim 1, .used in combination with apump impeller.

12. An inducer, as claimed under claim 1, used independently, withoutany additional pump impeller, and performing the duties ofa pumpimpeller.

